1. Field of the Invention
This invention relates to electronic apparatus and methods for the continuous and automatic testing of a unique data transmission system. More particularly, the invention relates to apparatus and methods for the automatic testing of cabling and data transmission components used in a complex system such as an aircraft simulator in a manner which is continuous (even during system operation) and inexpensive. The automatic testing capability also monitors and identifies system components still operating within tolerance but experiencing degradation in performance. Such monitoring allows timely maintenance to prevent catastrophic failure.
2. Description of the Prior Art
There are many and varied electronic systems presently in operation which require the transmission of vast amounts of information from a source (such as a computer) to individual load devices. As an example, the interconnection system of present-day aircraft simulators consists of a multitude of cables, patch panels or cabinets, individually wired back plates, and numerous series disconnects, all serving to tie together a complex consisting of widely separated components such as a computer, cockpit instruments and controls, instructor operator station, and several cabinets of signal conditioning and electronic conversion devices. This type of present-day simulator may well include over 2500 independent transmission channels (both analog and digital, but predominately analog), some of which are separated by distances greater than 100 feet. Some of the problems, such as the large amount of hardware and the interconnecting wiring associated with such a complex simulation system, are apparent by visual inspection. Two of these readily apparent problems which are significant include:
(a) the requirement of extensive use of interconnection cables and associated patch panels or cabinet assemblies; and PA1 (b) the frequent and necessary use of very long interconnecting cables, which use results in degradation of signal quality due to the noise picked up by the long cables.
For example, if an aircraft simulator complex using 2500 transmission channels, each requiring two wires which, on an average, cover a distance of fifty feet, then there would be on the average approximately fifty feet during which each 5000 wires was subject to outside interference or about fifty miles (80 kilometers) of wire subject to outside interference. Further, the transmission of analog signals through standard twisted pairs subjects the signal to outside influences due to distributed impedance, particularly where the signals change at a rapid rate. Thus, the long distance and the complicated wiring patterns involved introduce very unfavorable signal-to-noise conditions which are responsible for significant degradation of simulator performance.
However, what is not so readily apparent as the above-mentioned problems is the complex, time-consuming bookkeeping and signal documentation which is necessary to accomplish the wiring and to facilitate troubleshooting and maintenance. In addition troubleshooting and problem resolution usually require the system to be shut down. Additional penalties associated with the presently available interconnection systems are found when one considers the impact on manufacturing processes, inventory control, and maintenance tasks. Each of these tasks is based on (in fact, is hampered by) the prior art techniques used for packaging and interconnection. For example, equipment checkout and testing at the systems level cannot be accomplished unit simulator fabrication is almost complete and the necessary associated signal conditioning hardware and interconnecting cables have been installed.
In addition to the common interconnecting techniques of using a single transmission channel for each control signal or bit of data, some efforts have been made to provide better and more efficient systems. Patent Application Ser. No. 795,320 filed by Haas et al on the same date as this application provides a particularly valuable data transmission system which substantially eliminates many of the problems enumerated above. The present invention is particularly suitable for use with the system described in the co-pending Haas invention. Another data transmission system that provides significant improvement over the standard techniques of signal and data distribution is described in U.S. Pat. No. 3,848,230, issued to John F. Rehm and Evan E. M. Lloyd on Nov. 12, 1974. However, notwithstanding the advantages made possible by the co-pending Haas et al application or the Rehm et al patent over standard techniques, there is still a significant amount of hardware which requires periodic maintenance and testing as well as troubleshooting when a problem occurs.
More specifically, past techniques of maintenance and troubleshooting required point by point checking of each circuit element between the simulator digital computer and the end item loads and devices. Thus there were many functionalized equipment modules and components at various different locations, each of which had to be checked and each of which usually had to be out of operation during the check. Since each particular piece of equipment provided a certain type of signal processing or conditioning, the interconnection of several equipment modules was often necessary to completely process or condition a single signal which originated from one end item so that it would be compatible and suitable for use by the piece of equipment requiring the data or signal to continue operation. In such situations, it is not uncommon for the individual component to check out as acceptable but the overall circuit fails to function properly, therefore requiring component by component replacement of components which appear to be operating properly.